(Winner of the 2012 Pulitzer Prize and the National Book Critics Circle Award) In the late 1940s George Kennan wrote two documents, the "Long Telegram" and the "X Article," which set out the containment strategy that would define U.S. policy toward the Soviet Union. This alone would qualify him as the most influential American diplomat of the Cold War era, yet he was also an architect of the Marshall Plan, a prizewinning historian, and would become one of the most outspoken critics of American diplomacy, politics, and culture in the latter 20th century. Yale historian and National Humanities Medal recipient John Lewis Gaddis began this magisterial history almost 30 years ago, interviewing Kennan frequently and gaining such frank and detailed material that Gaddis agreed that the book would not appear until after Kennan's death.